The present invention relates to a system configuration and a control method of an asynchronous transmission mode (ATM) switching unit.
Since ATM switching technology is recognized as a switching method of a new generation by the International Telegraph and Telephone Consultative Committee (CCITT), research and development in this technology is being conducted by many organizations to realize a broadband integrated service digital network (ISDN).
In ATM communication, various kinds of traffic such as voice, data, and animation each having a different bearer speed and burst property are controlled collectively. Accordingly, there are problems in that the control of transmission lines be comes necessarily complicated, and that it takes much more time to set calls in the ATM switching unit than in a current switching unit. Besides, the resources of existing switching units (software) must be taken over efficiently by the new technology.
An example of the prior art technology in contrast with the present invention is a switching method utilized in a synchronous transmission mode (STM). FIG. 1 shows a general view for explaining an STM switching method.
An STM switching method is a time-divisional multiplexing method associated with frame synchronization. In this method, each interval, called a frame, has a time length of 125 .mu.s and is divided into a plurality of time slots of fixed length. Then, channel data corresponding to each user is divided and multiplexed at each position of a time slot.
In FIG. 1, on the receiving side, each of four channel data indicated by A, B, C1, and C2 is multiplexed by a switch SW1 each fixed length in a time divisional manner. On the sending side, the multiplexed data are separated by a switch SW2 which is operated synchronously with the switch SW1. Setting the number of frames based on data volume enables the transmission of a required volume of data in each channel.
As described above, in the conventional STM switching method, each medium, such as voice, data, animation, etc., is assigned automatically and physically a fixed band of a line. Therefore, the STM switching unit can control the transmission line only by physically determining the free/busy state of the input and output of the switch, and the control can be performed quite easily. Such control of the transmission line can be realized as executed by a call processor according to a call processing software (program).
FIG. 2 shows a general view for explaining an ATM switching method associated with the present invention. In the ATM switching method, information of each channel is divided into short blocks. A header is added at the head of each block to be transmitted sequentially. A block with a header is called "a cell". The ATM switching unit enables high speed switching and transmission to a correspondent in a unit of a cell by identifying the contents of a header of each cell using hardware capabilities. In the above described switching method, various kinds of traffic such as voice, data, animation, etc. each having a different bearer speed and burst property can be transmitted collectively.
The ATM switching unit manages bands taking bearer speed and burst property of information into account. Therefore, in the ATM switching unit, the management of the resources of switches in the transmission line becomes complicated when calculating the discard rate, delay time, etc. In the ATM switching unit, a high level of resource management in which one route is selected promptly from among a plurality of switching routes leading in the same output direction is indispensable for distributing a traffic load in a switch and for increasing use efficiency of each switch in the switching unit as much a possible.
Accordingly, such management can be performed by a call processor similar to that in a conventional STM switching unit taking a very long time, thereby causing degradation of the quality of services.
However, there are problems with the ATM switching unit in that the configuration of a transmission switch (ATM switch) is different from that of a switch in a conventional STM switching unit; and in that current call processing software must be modified on a large scale to realize the transmission line control process successfully on a call processor side because the ATM switching unit has different realizing methods and different switch controlling methods.
A similar problem occurs when a large scale ATM switching unit is realized.
Furthermore, in the above described transmission line control method, a unit cannot be extended easily as desired.